Process for manufacturing nitrates



June 9,- 1931. J. l. BRONN ET AL 1,809,191

PROCESS FOR MANUFACTURING NI TRATES Filed Jan 26, 1928 KCL Sham & CZ VAPor Sham.

HCI,

So'lui'a'on,

fl'eam Ni'fric' Acid. vpor Siphon /nrent0r:::

steam. For the is preferably use an apparatus according Patented June 9, 1931 UNITED STATES PATENT orrlcr.

JIiGOR ISRAEL BRONN, OF BERLIN -CHA.LOTTENBTIRG, AND GEORG FISCHER, OF OBER- .-HAUSEN, GERMANYi SAID FISCHER ASSIGNOR TO SAID BRONN PROCESS FOR MANUFACTURING NITRATES Application filed January 26, 1928, Serial No. 249,713, and in Germany January 24, 1927.

The present invention relates to the conversion of chlorides of alkali-forming metals, more particularly of sodium chloride and potassium chloride, into nitrates by treatment with nitric acid.

It is true that it has already been proposed to obtain nitrates in the above manner, for instance by treating solutions of potassium chloride" or of sodium chloride with nitric acid, and b crystallizing out the nitrates produced." t has been also attempted to distill oil the hydrochloric acid liberated in the process, which however means considerable losses of nitric acid.

It has now been ascertained that chlorides of alkali-forming metals can be easily converted into nitrates by treating these chlorides with vapors of nitric acid or with nitric oxides which are strongly diluted with urpose in question there to the accompanying drawing.

A tower-shaped container 1 of. earthenware or some other acid-proof material, provided at a certain distance from the bottom with a perforated bottom or grate 2 is filled with pieces ofpotassium chloride 3. Under the grate open several pipe branches. Through the pipe branch 4 are continuously admitted vapors of water-containing nitric acid, and through the pipe branch 5 is con tinuously admitted slightly superheated steam. The steam and the nitric acid could however be brought together beforehand and introduced through a common pipe.

It has now been ascertained that as the nitric acid vapor enters the potassium chloride charge, potassium nitrate is formed even' within the lower layers of the charge.

'As it is much more soluble in hot water than potassium chloride, the potassium nitrate thusformed will be dissolved much sooner by hot water "(from the steam), and the hot solution of almost pure potassium nitrate 6 will collect under the grate'2: it isintermittently or continuously discharged by means of a siphon 7 which is provided with a valve 8. This solution of potassium nitrate is concentrated to such a degree that on cooling it becomesa crystalline paste. By suitably dimensioning the height of the charging vessel 1, which must be adapted to the *nitric oxides. If the escaping acid vapors are given an opportunity to condense, there will be left already in the first condensing vessel a hydrochloric acid with about 15% HCl, and the escapingsteam will be practicall'y free from acid; by raising it to about 130 (3., it can be'usedagain in the process,

with the addition of fresh steam. This steam here functions so to say as a vehicle, as at first it conveys the nitric acid, then lixiviates the potassium nitrate and finally further conveys the hydrochloric acid. Only as much steam is consumed as required for dissolving potassium nitrate and nitric acid, the remaining steam to 75%) is left in circulation and merely, requires alwaiys to be heated again to about 130 C.

he process may be rendered a continuous one. The charging with solid potassium chloride may be effected by the well-known combination of a hopper with a worm conveyor 12 or by means of similarly acting auxiliary devices.

As a rule the proceeding must be such that there should be under the grate 2 a mixture of vapors which consists of about one part by weight of nitric acid and ten to fifteen parts'by weight of water: It has been found-that a temperature of 120130 C. is very favorable. At this temperature any slight quantities of potassium chloride that maybe contained in the solution 6, are

decomposed by the nitric acid atmosphere, and on the other hand the risk of the solu- 1 tible losses of nitric acid taking place. This process may likewise be converted into a continuous one, for instance by filling the tower 1 with acid-proof pieces or rings of ceramic material and by causing a more or less concentrated lye containing potassium chloride to trickle down. The rising mix- 'ture of nitric acid vapors and steam decompotassium chloride that may be contained therein.

-In working with salt brine it is advisable to keep the steam as hot as the nitric acid can stand without decomposing, and moreover to protect the reaction tower from loss of heat exte'rnall The quantity of steam can be reduced, or instance to eight parts by weight of steam to one part by weight of mtric' acid. Sometimes it is advisable to use for filling the reaction tower, salt in pieces or briquetted, over which thesalt brine trickles down. In this way the capacity of the tower is increased, and steam is economized as a consequence.

The hot solution which collects under the charging grate and consists chiefly or exclusively of dissolved nitrates is siphoned off and crystallized whether at rest or in motion. The siphoning can also be done continuously. The remaining mother-lye is either evaporated or, in the event of its still contaming chlorides, used again for chargingv the reaction tower.

The method of working which has been described here with reference to the treatment of potassium chloride, can also be used for the conversion of sodium chloride into sodium nitrate. The process can also be 5 extended to the treatment of crude potassium salts as will be described further on.

The process described may be modified in various ways. Thus for instance it is known that by simply pouring nitric acid over a potassium chloride solution, a crystalline paste is obtained which already contains nearly of the nitric acid .bound to potassium. If this crystalline paste is drawn off or centrifuged, a liquid will be left which contains about 20% undecomposed potassium chloride and an acid mixture of 20% nitric acid and 80% hydrochloric acid.v In certain cases it may be economical to combine the processes in such a manner that the solution which is separated from the crystalline paste and contains about 20% nitric acid, is carried together with fresh salt lye or pieces of salt, in the opposite direction to the rising nitric acid vapor-steam mixture. In this case however the solution which contains a mixture of free acids, must be, admitted throu h a separate branch at/ about the middle 0 ing column.

If the working is done with crude potassium salts, the process may be carried out in two ways: 1

The reaction tower described ,is charged with solid crude salt or with a solution of crude salt, or with both, for instance by causing a crude salt lye to trickle down over crude salt pieces. If the speed of the rising mixture of nitric acid vapors and steam is low, itis possible to ensure that all the constituents of the crude potassium salts (potassium, sodium, calcium, magnesium) will be converted to a greater or less extent into nitrates. The solution of all these nitrates, collecting under the grate of the reaction tower, can then be mixed in crystallization vessels with fresh crude salt potassium nitrate being chiefly crystallize out, and the other nitrates formed, being converted back to their chlorides. As a rule it is however preferable to so work that the rising mixture of steam and nitric acid converts only, or chiefly, potassium chloride alone into nitrate. This can be done by coordinating the temperature, concentration and velocity of flow of thenitric acid vapor mixture in such a manner that the dissolving action of this mixture is stronger than the nitrating action. In this way the salt to be treated will be dissolved to a greater extent than nitrated. Consequently in the trickling liquid, partly even before it reaches the height of the charg "the grate 2, there takes place already the reaction between any other nitrates carried by it and the potassium chloride that may still remain.

In all these processes, the degree of concentration of the original nitric acid is of little importance as it comes into action only after a strong dilution with steam. It is not therefore absolutely necessary to cause nitric acid in the form of vapors mixed with steam to act on the chlorides to be converted. Diluted nitric acid can be introduced, for instance in the middle of the reaction tower, whilst from the bottom would be supplied only superheated steam, owing to which losses by decomposition of nitric acid will also be avoided. Instead of pure or finished nitric acid, there may also be used suitable nitric oxides with air or with oxygen, that is to say mixtures produced in the burning of atmospheric nitrogen in electric arc furnaces or in the catalytic burning of ammonia. The presence of oxygen or air does not affect the process described. In connections herewith it may however be stated that although dilution of the nitric acid or nitric oxides is not excluded, in connection with the process of this invention, such dilution is not adapted to substitute the dilutionwith copious quantities of steam. Experience has shown that nitric acid when brought to reaction with alkali metal chlorides, if usedin a concentrated condition or diluted with -air, tends to react with the formed hydrochloric acid, so as to. liberate chlorine. Thereby the process is made not only uneconomical but above all the hydrochloric acid is spoiled and there results a .10 highly deteriorating. effect on the reaction vessels. This drawback can only be avoided by dilution of the nitric acid (or' oxides) with copious quantities of steam as taught by thisinvention. i 4

If it is found that the finished product, in thepresent case saltpeter,'contains some free acid which is chiefly injurious, to the .durability of the packing, it is advisable to neutralize the free acidby the addition of tiny quantities of lime or alkalies or carbonates. As the nitrates thus produced arechiefly used for manuring, slight admixtures of other salts or of undecomposed chlorides are of no importance. I

The economic importance of .the present process for agriculture is that it makes it possible to obtain directly such high grade manures as sodium nitrate .(Chile saltpeter) and potassium nitrate (potash saltpeter) from their chlorides or brinesor'from crude salt without any loss of nitric acid.

Where the .term oxides of nitrogen is used in the appended claims, we mean to com-prise the hydrates thereof or in other words the acids directly derived from said oxides as well as the oxides themselves.

Furthermore, in the accompanyingclaims by of the vapors of nitric acid.

3. Process of manufacturing nitrates comprising reacting on pieces of salt comprising chlorides of alkali-forming metals wetted by salt brine with nitric acid in the presence of copious quantities of steam.,

4. Process of manufacturing nitrates comprising reacting on crude salt containing chlorides of alkali-forming metals with 0x ides of nitrogen in the presence of copious quantities of steam.

1 5. Process of manufacturing nitrates com prising reacting on chlorides of alkali-forming metals with nitric acid, recovering the nitrate formed thereby and treating the to include the alkali metals and' alkaline mother liquor in counter-current with a mixture of nitric acid and copious quantities of steam.

6. Process of manufacturing nitrates com-' prising reacting on chlorides of alkali-forming metals with oxides of nitrogen in the presence of copious quantities ofsteam and neutralizing the excess acid in the formed nitrate with an alkaline substance.

7. Process of manufacturing nitrates comprising introducing oxides of nitrogen and copious quantities of steam near the bottom of a reaction tower filled with solid chlorides of alkali-forming metals supported on "a. grate, removing the exhaust gas at the top of the tower and recovering nitrate solution collecting at the bottom of the tower.

8. Process of manufacturing nitrates comprising treating chlorides of alkali-forming metals with oxides of nitrogen in. the pres ence of copious quantities of steamat a temperature above the boiling point of aqueous hydrochloric acid of highest .possible concentration.

9. Process of manufacturing nitrates comprising treating alkali metal chlorides with oxides of nitrogen in the presence of copious quantities of steam.

. 10. Process of manufacturing nitrates comprising treating alkali metal chlorides with a mixture of nitric acid vapors and steam, the'quantity of steam being a multiple by weight of the quantity of nitric acid vapors.

11. Process of manufacturing nitrates comprising reacting 'on pieces of alkali metal chlorides wetted by alkali metal chloride brine with nitric acid in the presence of copious quantities of steam.

12. Process of manufacturin nitrates comprising reacting on crude al ali metal chlorides with oxides of nitrogen in. the presence of copious quantities of steam.

13. Process of manufacturing nitrates comprising reacting on alkali metal chlorides with nitric acid, recovering the nitrate formed thereby and treating the mother liquor in counter-current with a mixture of nitric acid and copious quantities of steam.

14. Process of manufacturing nitrates comprising reacting on alkali metal chlorides with oxides of nitrogen in the presence of copious quantities of steam and neutralizing the excess acid in the formed nitrate with an alkaline substance.

15. Process of manufacturing nitrates comprising introducing oxides of nitrogen and copious quantities of steam near the bottom of a reaction tower filled with solid alkali metal chlorides supported on a grate, removing the exhaust gas at the top of the tower, and recovering nitrate solution collecting at the bottom of the tower.

16. Process of .manufacturing nitrates comprising treating alkali metal chlorides with oxides of nitro en in the presence of copious quantities o steam at a, temperature above the boiling oint of a ueous hydrochloric acid of tration.

-17. Process of "manufacturin nitrates which comprises treating an al ali metal chloride with oxides of nitrogen in the pres ence of copious quantities of superheated. steam.

18. Process of manufacturin nitrzites which comprisestreating an al ali metal chloride with oxides of nitrogen in the pres ence of copious quantities of superheated 5 steam at a temperature of about 120-l30 C.

In testimon whereof I afiix my signature.

EGOR ISRAEL BRONN. .In testimony whereof I afiix my signature:

DR. GEORG FISCHER.

hlgl iest possib e concen- 

